Measuring and testing – Tire – tread or roadway – Tire inflation testing installation
Patent
1985-02-27
1985-10-08
Caldwell, Sr., John W.
Measuring and testing
Tire, tread or roadway
Tire inflation testing installation
340 52B, 340 52R, 303105, 73 9, B10G 1910
Patent
active
045452407
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to apparatus to determine the adhesion factor of a wheel of a vehicle on a road surface, and more particularly to detect slippage or incipient slippage of a wheel with respect to a road surface, especially to determine aquaplaning of automotive wheels on a road surface.
BACKGROUND
In vehicles, especially road vehicles, devices are becoming increasingly well known which indicate the status of the road to the driver. Among these are ice warning indicators used together with on-board computers which trigger a warning indication within a temperature range in which icy road surfaces can be expected. However, these ice warning indicators have the disadvantage that although they do indicate the critical ambient temperature range, they provide no information as to the actual state of the road surface at that time or as to the road surface adhesion factor which is of importance in terms of the drivability of the road, because the adhesion factor does not automatically and directly vary with the ambient temperature.
The provision of devices indicating aquaplaning has also been proposed; such devices trigger a warning whenever a wheel, because of aquaplaning, loses its capacity to transmit friction to the road surface and thus loses peripheral velocity. Tests with various vehicles and various tires have demonstrated, however, that the state of aquaplaning, which is extraordinarily critical for vehicle controllability, occurs within a very narrow velocity range. The above-mentioned decrease in peripheral velocity occurs at a velocity which is only a few percent below a threshold velocity at which the wheels, due to aquaplaning conditions, are no longer capable of transmitting frictional forces. As a consequence, the aquaplaning warning comes, effectively, too late.
It is known to equip vehicles having power-assisted brakes with antiskid brake systems, that is, systems which by means of transducers ascertain variables during driving. Control variable signals are derived from the variables for varying the braking pressure. Such antiskid brake systems are described, for example, in "Bosch Technische Berichte" [Bosch Technical Reports], volume 7 (1980), No. 2 or in SAE Technical Paper No. 790458.
THE INVENTION
It is an object to provide an apparatus which will indicate to an operator of a vehicle whether a wheel is gripping a road surface, or may slip with respect thereto, for example to determine if a wheel is aquaplaning over a wet road surface. In effect, the method and apparatus determines the adhesion factor of the wheel with respect to the road surface.
The term "slip" will be used herein. Slip, in the field to which the present invention relates, is usually stated as follows, e.g. in the relevant literature: velocity of the wheel under consideration for slippage.
Brake slip is defined in the range of from 0% to 100%. A freely rolling unbraked wheel has a slip of 0%; a locked wheel has a slip of 100%. Actual slip is the slip of the wheel with respect to a road surface, and in limiting cases, again, a freely rolling wheel, on a gripping surface, will have a slip of 0%, whereas a locked wheel will have a slip of 100%. Intermediate the limiting values, the brake slip and the actual slip may, however, differ. For a detailed discussion of slip in connection with braking of vehicle wheels, reference is made to "Bosch Technische Berichte" [Bosch Technical Reports], English special edition of February 1982, "Antiskid System (ABS)", of which the present inventor is a co-author, pages 65 to 93, copy in the library of the U.S. Patent and Trademark Office.
Briefly, in accordance with the present invention, the brakes of a vehicle are actuated, either automatically or under operator control, to apply a predetermined and low pressure to the wheel of the vehicle, and then measure the deceleration of the wheel. If the deceleration of the wheel corresponds to the expected deceleration of the vehicle due to the braking, an indication is available that the surface on which the wheel runs is a good o
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Literature Reference "Prufprogramm".
Caldwell Sr. John W.
Heim Michael F.
Robert & Bosch GmbH
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